3. Energycushman/books/Numbers/Chap3-Energy.pdffollowing 4 weeks [17, page 118]. The volume to mass...
Transcript of 3. Energycushman/books/Numbers/Chap3-Energy.pdffollowing 4 weeks [17, page 118]. The volume to mass...
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3. Energy 3.1. Units Energy is probably the physical quantity with the most diverse set of units at our disposal, allowing us to quantify a wide range of amounts from the tiny energy of a single electron to the amount consumed annually in the world. Units also tend to differ depending on the context, not being the same for electricity, petroleum, food, thermal engines, and buildings. Below are the main units in alphabetical order [1]: 1 BOE (barrel‐of‐oil‐equivalent) = 5.80 x 106 BTUs = 6.1179 x 109 J = 1,699 kWh 1 BTU (British Thermal Unit) = 1,055.056 J = 2.92875 x 10‐4 kWh = 251.996 cal 1 cal (calorie) = 0.003968 BTUs = 4.186 J 1 EJ (exa‐joule) = 1018 J = 9.478 x 1014 BTUs 1 erg = 10‐7 J 1 eV (electron‐volt) = 1.60218 x 10‐19 J 1 GJ (giga‐joule) = 109 J = 947,820 BTUs = 277.78 kWh 1Gtoe (giga‐tonne of oil equivalent) = 1,000 Mtoe = 41.868 EJ = 39.68 quads 1 J (joule) = 0.00094782 BTUs = 0.2389 cal 1 kJ (kilo‐joule) = 1,000 J = 0.947813 BTUs = 238.84 cal 1 kcal (kilo‐calorie) = 1 food calorie = 1000 cal = 3.9683 BTUs = 4,186.8 J 1 kWh (kilo‐watt‐hour) = 3,412.1 BTUs = 3.600 MJ = 859.9 kcal 1 lb‐steam (pound of steam) = 970 BTUs 1 MMBTU = 1 MBTU = 106 BTUs = 1.055056 x 109 J = 293.07 kWh 1 MJ (mega‐joule) = 106 J = 947.82 BTUs = 0.27778 kWh 1 Mtoe (million tonne of oil equivalent) = 4.1868 x 1016 J = 1.163 x 107 MWh 1 MWh (mega‐watt‐hour) = 1,000 kWh 1 Q (quad) = 1015 BTUs = 1.055056 EJ 1 Therm = 100,000 BTUs 1 Wh (watt‐hour) = 3.412 BTUs = 3.600 kJ = 859.9 cal Power, which is energy per time, tends to have some units of its own [2]: 1 hp (horsepower) = 2,542.47 BTUs/hour = 745.70 W 1 W (watt) = 1 J/s = 3.4121 BTUs/hour = 1.341 hp 1 kW (kilo‐watt) = 1,000 W 1 MW (mega‐watt) = 106 W 1 GW (giga‐watt) = 109 W 1 Ton (ton of refrigeration) = 12,000 BTUs/hour = 3,516 W
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3.2. Solar energy The temperature of sun is 5,778 K = 5,505oC. The solar radiation shining at the top of the atmosphere is 1,367 W/m2 (±3% as the earth orbits the sun) [3] and spans a spectrum from about 200 nm (nanometer) to 4,000 nm, with peak around 550 nm, consisting of 10% ultraviolet (UV), 40% visible light, and 50% infrared (IR) [4]. Visible light has wavelengths from 380 (red) to 780 nm (violet) [4]. After adjustment for angle of incidence and lack of radiation at night, the solar flux averaged over the earth's surface is 340 W/m2 of which 48% or 163 W/m2 reaches the earth’s surface [5]. A “peak‐sun” is defined as 1,000 W/m2, which is about what a mid‐latitude location receives at noon when the sky is clear. The amount of solar energy reaching the earth every hour (628 EJ) is greater than the amount of energy consumed by the whole human population over an entire year (389 EJ in 2013 [6]). 3.3. Energy generation From Albert Einstein, we know that mass can theoretically be converted into energy according to E = mc2. This formula provides a theoretical maximum for energy extraction per mass: E/m = c2 = 89.9 x 109 MJ/kg. Needless to say, fuels used by humans fall far short of this theoretical limit, as the numbers below indicate. Of the total primary energy supply in the world in 2014, 81% is from carbon‐based fossil sources divided in oil (31%), coal (29%) and gas (21%). Next sources are biofuels & waste (10.1%), nuclear (4.8%), hydro (2.4%), and other renewables (1.3%) [6]. 3.3.1. Solid fuels The amount of thermal energy released by the combustion of the most common solid fuels is tabulated below. Energy released by combustion (MJ/kg) (BTUs/lb)
Cardboard 16 – 19 6,900 – 8,200
Coal
anthracite 30.1 12,910
bituminous coal 25.0 – 33.4 10,750 – 14,340
charcoal 28 12,000
lignite (“brown coal”) 16.1 6,910
peat 21 9,000
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Nuclear 235U in theory1 83,140,000 3.57 x 1010 235U in burner reactor 500,000 2.15 x 108
Paper 16 – 19 6,900 – 8,200
Plastics
polyethylene 45 19,400
polypropylene 45 19,400
polystyrene 40 17,200
PVC (bottles, etc.) 15 – 25 6,500 – 10,700
Solid waste
municipal garbage 20 8,600
animal dung 10 4,300
dried bagasse 16 6,900
food scraps 15 – 20 6,500 – 8,600
rice husks 16 6,900
shelled corn 392,000 BTUs/bushel2
Switchgrass (oven dried) 18.0 7,750
Wood
green (50% MC)3 10.0 4,300
semi‐dried (30% MC)3 14.0 6,020
air‐dried (20% MC)3 16.0 6,880
oven dried (0% MC)3 20.0 8,600
seasoned 20 x 106 BTUs/cord4
wood pellets 15.8 6,800
premium wood pellets 19.1 8,200 Sources: [7, 8, 9, 10, 11] 1 The fission of one atom of Uranium‐235 generates 3.24 x 10‐11 J, which amounts to 83.14 TJ/kg. 2 1 bushel = 64 US pints = 35.2 L. 3 MC = Moisture Content, on wet basis. 4 A cord of wood is 8ft x 4ft x 4ft, including spaces between logs. A typical woodstove is only 65‐75% efficient; a pellet stove is 83% efficient; the rest of the heat goes out the chimney with the smoke.
In the United States in 2013, 80 waste‐to‐energy plants incinerated 30 million tons of municipal solid waste and generated 14 billion kWh of electricity, about the same amount used by 1.3 million households [12]. 3.3.2. Liquid fuels One barrel of oil, which holds 42 US gallons = 0.159 m3, weighs 136 kg and has an energy content of 5.80 x 106 BTUs = 6.12 GJ [13]. Equivalently, 1 metric ton of crude oil holds 42.65 x 106 BTUs = 45.00 GJ in the form of chemical energy. Below are the energy contents of the most common liquid fuels. Energy released by combustion (MJ/kg) (MJ/L) (BTUS/gallon)
Biodiesel 35.6 128,000
Crude oil 45 38.4 138,000
Diesel 50 38.7 139,000
Ethanol 30 23.6 84,530
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Fuel oil #2 40 36.7 138,800
Fuel oil #6 45 41.8 150,000
Gasoline (“petrol”) 48 34.6 124,000
Kerosene 44 37.6 135,000
Liquified natural gas (LNG) 55 23,700 BTUs/lb
Liquified propane (LPG) 46 25.5 91,330
Methanol 23 18.2 65,200 Sources: [9, 10, 13, 14, 15]
3.3.3. Gaseous fuels Since gases are compressible, their energy content is best quoted on per‐mass basis. Energy released by combustion (MJ/kg) (BTUs/lb)
Biogas 45 19,300
Butane 50.3 21,640
Hydrogen 142.1 61,084
Methane 55.4 23,811
Natural gas 45.4 – 52.3 19,500 – 22,500
Propane 50.2 21,564 Sources: [9, 16]
On a volume basis at ambient temperature, natural gas holds 1,025 BTUs/ft3 (= 38.2 MJ/m3) [10]. This makes 106 ft3 (= 28,320 m3) of natural gas is equivalent to 177 barrels of crude oil. At standard compression for delivery trucks, propane holds 91,300 BTUs/gallon (= 25.4 MJ/L) [10]. 3.3.4. Compost Compost can be used to heat or pre‐heat water for domestic consumption. A compost heap generates heat at the rate of 1,500 BTUs/hr per short ton of material (= 1,740 J/hr/kg) for the first 4 weeks and 500 BTUs/hr per short ton (= 580 J/hr/kg) for the following 4 weeks [17, page 118]. The volume to mass ratio is 2 cubic yards per short ton (= 1.7 m3 per metric ton). Typical temperatures inside a compost heap are 120‐130oF (= 50‐55oC) toward the bottom of the heap and 150‐180oF (= 66‐82oC) toward the top (because hot air rises), regardless of the outdoor atmospheric temperature [17, page 117]. The outputs from 1 metric ton (2,205 lbs, including 50% by weight) of compost are 3.375 MBTUs, 290 kg of CO2 and 47 liters of water vapor over the course of a 21‐day thermophilic stabilization period. These are equivalent to 1,530 BTUs, 0.29 lb CO2 and 0.0056 gal of water vapor, per pound of compost [18]. 3.3.5. Animal manure
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A composting system designed for small farms or homesteads claims an output of 50,000 BTUs/hr generated from 30 to 50 short tons of animal manure made available every 8 weeks, the equivalent of 12 to 20 cows or horses [17, page 145]. In composting farmyard manure, bacteria generate 4.03 kWh per kg of oxygen consumed (= 6,240 BTUS/lb O2 = 14.5 MJ/kg O2) [19]. 3.3.6. Other biological matter Thermophilic bacteria generate 4 Wh per gram of oxygen used (= 6,190 BTUs per pound of O2 = 14.4 MJ per kg of O2) [20]. 3.3.7. Photovoltaic cells There are many different types of photovoltaic (PV) cells available on the market, and each type has its own efficiency, as shown in the graph below [21]. The 2015 efficiency of the typical crystalline silicon PV cell used in roof‐top applications is 12‐15% installed [21]. Figure 1. Confirmed conversion efficiencies for a variety of photovoltaic technologies, from 1976 to 2015, at a reference temperature of 25oC.
Source: [21]
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The energy output of a photovoltaic cell depends on various factors. Considering a final 12% conversion efficiency, the average annual energy output of a photovoltaic cell is 216 kWh/m2 per year in the continental U.S. [22], 79 kWh/m2 in Alaska, and 280 kWh/m2 in the Sahara [23, page 343]. 3.3.8. Wind turbines The table below provides the wind power density (Watts per square meter of area swept by the turbine blades) as a function of wind speed [24]. In wind energy, it has become traditional to ascribe “wind power class” numbers to various wind speed intervals based on height above the ground (= level of turbine nacelle). Physics dictate that the power in the wind increases like the cube of its speed.
Wind power class
10m 30m 50m
Power density (W/m2)
Speed (m/s)
Power density (W/m2)
Speed (m/s)
Power density (W/m2)
Speed (m/s)
1 0‐100 0‐4.4 0‐160 0‐5.1 0‐200 0‐5.6
2 100‐150 4.4‐5.1 160‐240 5.1‐5.8 200‐300 5.6‐6.4
3 150‐200 5.1‐5.6 240‐320 5.8‐6.5 300‐400 6.4‐7.0
4 200‐250 5.6‐6.0 320‐400 6.5‐7.0 400‐500 7.0‐7.5
5 250‐300 6.0‐6.4 400‐480 7.0‐7.4 500‐600 7.5‐8.0
6 300‐400 6.4‐7.0 480‐640 7.4‐8.2 600‐800 8.0‐8.8
7 400‐1000 7.0‐9.4 640‐1600 8.2‐11.0 800‐2000 8.8‐11.9 Source: [24]
3.4. Energy conversion 3.4.1. Electricity generation A traditional thermal power plant is 33.2% efficient and produces 1 kWh of electricity from 10,292 BTUs of thermal energy [25], which amounts to about 11 GWyr (giga‐watt‐year = 8.76 x 109 kWh) for every quad of fuel. In the USA, the generation of 1 kWh of electricity necessitates 95 L of water in average, with a low of 0.038 L/kWh for electricity from natural gas to a high of about 420 L/kWh for electricity from biodiesel [26]. 3.4.2. Internal combustion engine The internal combustion engine (ICE), propelling most cars, trucks and boats, is about 30% efficient [27]. For an automobile, after subtraction of parasitic losses (such as alternator, water pump, headlights, drivetrain losses, idling, etc.), the energy delivered
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to the wheels to move the vehicle is only 18‐25% of the chemical energy held in the fuel, as the figure below illustrates.
Source: [27]
A 2004 study published in Science [28] calculates a tank‐to‐wheel efficiency of 12.6% for a 1,500 kg ICE car (lower than the range quoted above) and 27.2% for the hybrid‐ICE car (above the range quoted above). When the internal combustion engine is used as an electric generator (for off‐grid applications or during emergencies, for example), it consumes 10,403 BTUs of petroleum fuel per kWh of electricity generated [25]. 3.4.3. Electric motor / Alternator In contrast to the internal combustion engine, the electric motor is far more efficient, at 87%, with the most powerful ones exceeding 90% [29]. When used in reverse as an alternator, the efficiency is about the same. The company Tesla claims on its specs page that the 270/310 kW (= 362/416 hp) AC motor in its 85 kWh Model‐S automobiles is 92% efficient [30]. After drivetrain and parasitic losses, this translates into 0.25 kWh per mile of driving at 50 mph (= 80 km/h) [31]. However, one needs to keep in mind that the generation of electricity upstream of
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the car is a very inefficient process (see Section 3.4.1 above) and that the efficiency of an electric motor depends on its speed and torque. 3.4.4. Fuel cells The Proton‐exchange‐membrane (PEM) fuel cell, which produces electricity from hydrogen at ambient temperatures, is about 40‐50% efficient [28, 32]. A PEM fuel‐cell car has an estimated tank‐to‐wheel efficiency of 26.6% [28]. The table below compares the efficiencies of various fuel‐cell technologies.
Fuel cell technology Efficiency With co‐generation of heat
Alkaline 60‐70%
Direct methanol < 40%
Molten carbonate 65% > 85%
Phosphoric acid 37‐42% > 85%
Proton exchange membrane 40‐50%
Solid oxide 60‐70% up to 85% Sources: [28, 32, 33]
3.4.5. Biomass to ethanol Ethanol can be produced from a variety of organic materials (biomass). The table below recapitulates the theoretical yields for the most common feedstocks. For conversion from volume to mass, use ethanol density of 0.789 kg/L.
Feedstock Theoretical Ethanol Yield
(gallons per dry ton) (L/kg)
Bagasse 111.5 0.465
Corn grain 124.4 0.519
Corn stover 113.0 0.472
Cotton gin trash 56.8 0.237
Forest thinnings 81.5 0.340
Hardwood sawdust 100.8 0.421
Mixed paper 116.2 0.485
Rice straw 109.9 0.459
Switchgrass 96.7 0.404
Wood 100.2 0.418 Sources: [34]
Ethanol can also be produced from algae in a body of water exposed to sunlight and atmospheric carbon dioxide. An experimental program reported producing 9,000 gallons of ethanol per acre per year (= 84 m3 per hectare per year) [35].
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Fermentation of sugar in sweet beets yields 1,000 gallons of ethanol per acre based on a harvest of 35 tons per acre [36]. 3.4.6. Oil crops to biodiesel Biodiesel is a renewable fuel that can be produced from naturally oily plants, particularly oil palm. Oil palm trees produce 20 metric tons of fresh fruit per hectare per year, of which the oils form 10% of the total dry biomass while the remaining 90%may serve as a source of fiber or cellulosic material for additional biofuel production [37]. The table below compares the yield from various crops, including oil palm, which has the highest yield.
Plant Biodiesel Yield
(L/hectare) (gallons/acre)
Coconut 2,160 231
Oil palm 4,800 520
Peanut 820 88
Rapeseed 936 100
Soybean 526 56
Sunflower 760 81 Source: [37]
3.4.7. Efficiency factors The table below recapitulates the approximate efficiency factors for various types of energy conversion. From To By means of Efficiency Source
Biomass
Electricity Gasification + gas turbine + generator 20% [40]
Gas Integrated gasification 45% [40]
Heat Woodstove (with smoke up chimney) 65‐83% [41]
Coal Electricity Power plant via steam 33‐37% [38],[43]
Heat Home coal furnace (with vented smoke) 55% [39]
Diesel Electricity Stationary diesel generator 40% [43]
Mechanical Automotive diesel combustion engine 40‐48% [44]
Electricity
Heat Electric resistance 100% [39]
Hydrogen Electrolysis 81% [38]
Light1
Incandescent bulb 5% [39]
Fluorescent lamp 20‐25% [39]
Light‐emitting diode (LED) 50% [42]
Mechanical Electric motor 80‐93% [29]
Fossil fuel Heat Combustion 100% ‐‐
Combustion (with vented smoke) 65% [39]
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Gasoline Electricity Generator 18‐20% [43]
Mechanical Internal combustion engine 30% [27]
Hydro Electricity Water turbine + generator 93% [43]
Hydrogen Electricity PEM fuel cell 40‐50% [28],[38]
Phosphoric acid fuel cell 65% [33]
Mechanical Electricity Generator / Alternator 90‐95% [39]
Natural gas
Mechanical Gas turbine 50‐60% [43]
Electricity Gas turbine + generator 50% [43]
Heat Home gas furnace 85% [39]
Nuclear Electricity Uranium fission + steam cycle 33% [43]
Solar light Biomass Photosynthesis 3‐6% [45]
Electricity PV cell 3‐22% [21]
Steam Heat Boiler 85% [39]
Mechanical Steam turbine 45% [39]
Wind Electricity Wind turbine + generator 25‐35% [38]1 Based on 200 lumens = 1 W of emission in the visible spectrum
3.5. Energy storage 3.5.1. Batteries Three quantities best describe the capability of a battery: Its energy density (measuring how much energy can be stored per mass of battery, sometimes also called specific energy), its power density (measuring how quickly the energy can be retrieved from the battery), and its round‐trip efficiency (ratio of electricity recovered to electricity stored, also called Coulombic efficiency). The table below compares these numbers for a variety of commercially available batteries.
Battery Energy density
(Wh/kg) Power density
(W/kg) Round‐trip efficiency
Lead‐Acid 35 180 >80%
Lithium‐Ion 118 ‐ 225 200 ‐ 430 >95%
Lithium‐Ion Polymer 130 ‐ 225 260 ‐ 450 >91%
Nickel‐Cadmium 50 ‐ 80 200 75%
Nickel‐Metal Hydride 70 ‐ 95 200 ‐ 300 70%
Redox Flow 10 ‐ 50 >50 85%
Sodium‐Nickel Chloride 90 ‐ 120 155 80%
Sodium‐Sulfur 150 ‐ 240 150 ‐ 230 80%
Vanadium redox flow 50 110
Zinc‐Bromine 65 ‐ 75 90 ‐ 100 88‐95%
Zinc‐Air 294 ‐ 442 100 Source: [46 Table 1, 47 Table 37.2, 48 Table 1, 49]
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For comparison, the energy density of gasoline 12,890 Wh/kg [13], then reduced to 3,900 Wh/kg at the shaft because of the poor 30% efficiency of the internal combustion engine [27], and its power density easily exceeds 1,000 W/kg (= horsepower rating of the engine divided by its mass). The round‐trip efficiency of gasoline is 0% since the engine is incapable of converting mechanical energy back into fuel energy. The 85‐kWh Lithium‐ion battery set on board the 2012 Tesla Model S is reported having the following characteristics [50]: 140 Wh/kg energy density, 516 W/kg power density, and 75% round‐trip efficiency. The figure below, called the Ragone Plot, displays graphically the comparison between various types of energy storage: commercially available batteries, super‐capacitors, flywheels, fuel cells, and fossil fuels, based on energy density and peak power. Note the logarithmic scale of each axis.
Source: [51 Figure 38]
3.5.2. Hydrogen Being a gas that can be relatively easily generated and consumed, hydrogen may be used as a form of energy storage. Since its chemical energy content (see Section 3.3.3. above) is 142.1 MJ/kg (= 39.5 kWh/kg), any hydrogen system will necessarily have an energy density lower than 39.5 kWh/kg.
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For most applications, hydrogen may not be stored at ambient pressure but must be greatly compressed, liquefied, or stored in a metal hydride. Compression and liquefaction entail a significant energy penalty whereas storage in a metal hydride adds mass to the system. Thus, either way, the energy density of a complete system falls far below the theoretical maximum. The table below shows the energy density of systems as of 2006, per mass and per volume.
Technology Energy density
(kWh/kg) (kWh/L)
Compressed to 5,000 psi (34.5 MPa) 1.9 0.5
Compressed to 10,000 psi (69 MPa) 1.6 0.8
Liquified 1.7 1.2
Stored in metal hydride 0.8 0.6 Source: [52]
For hydrogen produced by electrolysis and converted back to electricity, the round‐trip efficiency is the efficiency of electrolysis times that of a proton‐exchange membrane fuel cell, that is, 0.81 x 0.45 = 36%. By contrast, the round‐trip efficiency of storing hydrogen in a metal hydride (Mg + H2gas ↔ MgH2) is around 74% [53] and can reach 90% for storage in metal organic frameworks (MOFs) [54]. 3.5.3. Pumped hydro Pumped hydro entails the pumping of water from a lower to a higher reservoir during energy storage and the release of this water back to the lower reservoir through a water turbine during energy recovery. The technology is mature and permits the storage of large quantities of energy but is applicable only where land is suitable and when energy release occurs over hours or days. Some systems have been in existence for since the 1920s. According to a 2013 Sandia National Laboratories report [55, page 33], systems can be sized up to 4,000 MW and operate with round‐trip efficiencies of 76% to 85%. A reservoir 25 m deep and 1 km in diameter situated 200 m higher than another reservoir (or natural lake) can hold enough water to generated 10,000 MWh. 3.5.4. Compressed air Compressing air to store energy entails a certain amount of adiabatic temperature increase depending on the rapidity of compression. A subsequent cooling to return the temperature to the ambient value during the storage period causes a heat loss, which may not be recovered during expansion. There is also some mechanical inefficiency in the compressor itself.
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A system storing air at 4,500 psi above atmospheric pressure (psig) can hold 22 to 49 Wh/L [53, page 14], which is much less than batteries, with a theoretical round‐trip efficiency ranging from 8% for isentropic (= rapid) compression and expansion to 72% for a three‐stage polytropic compression and three‐stage polytropic expansion [56, page 27], and up to 82% with great care [56, page 19]. 3.6. Energy transport 3.6.1. Electrical transmission Electricity is easily transported by electrically conductive wires. Depending on the voltage of the line, two stages are distinguished: transmission (at high voltage over long distances) and distribution (at low voltage across communities). A percentage of loss is quoted for the combination of transmission and distribution. Values depend on the quality of the infrastructure and the geographical distances in the country.
Region Country Transmission and distribution losses
North America
Canada 8.6%
Mexico 14.3%
United States 6.0%
Latin America
Argentina 16.0%
Brazil 16.4%
Cuba 15.4%
Haiti 54.2%
Latin America & Caribbean combined 14.8%
Europe
Belgium 4.9%
Denmark 5.5%
Central Europe & Baltics 7.5%
Finland 3.7%
Germany 3.9%
Italy 7.4%
Netherlands 4.4%
Norway 8.0%
Spain 9.0%
United Kingdom 7.5%
Africa
Algeria 18.4%
Kenya 18.0%
Nigeria 15.3%
Senegal 16.0%
South Africa 8.5%
Sub‐Saharan Africa 11.8%
Middle East Arab World 11.9%
Israel 4.0%
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Saudi Arabia 7.0%
Middle East & North Africa 12.0%
Central Asia Russia 10.1%
South Asia India 18.5%
Overall 18.1%
East Asia
China 5.8%
Japan 4.6%
East Asia & Pacific Islands 6.1%
Oceania Australia 5.9%
New Zealand 6.7%
World average 8.2% Source: [57] (2013 data)
3.6.2. Pipelines & oil tankers Conveying petroleum or natural gas by means of a pipeline over long distances requires pumping and thus entails an energy penalty. Pressure drop is caused by friction along the inner pipe walls as well as in bends, expansions and contractions because of secondary motions. Along natural gas pipelines, compressors that operate on a non‐stop basis are needed every 50 to 100 miles (80 to 160 km) to maintain adequate pressure. The average pumping station, utilizing multiple compressors for a total of 9,984 hp (= 7.45 MW) in average per station, is capable of moving 461 million cubic feet of natural gas per day (= 13.1 x 106 m3/day) [58]. This amounts to 21.6 hp per million cubic feet of gas moved per day (= 0.57 W per (m3 per day)). Assuming that the average distance between consecutive pumping stations is 75 miles (= 121 km), the power necessary to keep the gas moving per unit distance is 0.29 hp per million cubic feet conveyed per day over 1 mile, or 4.7 kW per million m3 conveyed per day over 1 km. In terms of energy expenditure per distance per mass of gas, the number is 1.7 MJ/km per metric ton of gas conveyed in the pipeline [59]. The 764 km long (= miles) Iraq Crude Oil Pipeline connecting the South Rumaila oil fields to the Red Sea has 6 intermediate pumping stations each equipped with 3 turbo‐pumps driven by 22 MW turbines, for a total maximum pumping power of 396 MW [60]. Assuming that this maximum power is consumed only when the pipeline is utilized at full capacity of 1.6 million barrels per day (= 2.94 m3/s), the power consumption is estimated at 176 kW per m3/s conveyed over 1 km. Further taking that crude oil has an energy content of 38.4 MJ/L (Section 3.3.2. above), the relative energy loss in pipeline transportation is 0.46% per 1,000 km (meaning that it takes 0.46 J to carry 100 J worth of crude oil over 1,000 km). In terms of energy expenditure per distance per mass of oil, the number is 0.2 MJ/km per metric ton of oil conveyed in the pipeline [59].
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Crude oil is also transported across the oceans by oil tankers. Using 0.16 MJ of energy needed to transport 1 metric ton over 1 km by means of an ocean ship [61, page 142] and the fact that crude oil contains 45 MJ per kilogram (Section 3.3.2. above), it is found that the energy efficiency of ocean shipping is 0.36% per 1000 km (meaning that it takes 0.36 J to carry 100 J worth of crude oil over 1,000 km). 3.7. Energy consumption 3.7.1. Transportation Energy for transportation is quantified as the energy needed to convey a certain number of passengers or tonnage of goods for a certain distance by a certain mode of transport. The numbers can be found in Chapter 5 together with the corresponding greenhouse gas emissions. 3.7.2. Buildings In the United States, it was estimated in 2014 that the electricity consumption in a residential home was 10,932 kWh per year in average, ranging from a low of 6,077 kWh/yr in Hawai’i (where the climate is very mild) to a high of 15,497 kWh/yr in Louisiana (where much electricity is used in summer for air conditioning) [62]. Since energy (kWh) divided by time (year) is power, this amounts to: 1.25 kW/home for the nation, 1.77 kW/home in Louisiana, and 0.69 kW/home in Hawai’i. Beware of the numbers used by some environmental organizations, in newspapers and magazines, and in advertisements, for they are often skewed! For large‐scale energy projects such as concentrated solar systems or wind farms, an accurate translation of power generated into number of homes being powered should take into account the fact that approximately 6% of the electrical power is lost in transmission and distribution [63]. This means that, because of transmission and distribution losses, 6% fewer homes can actually be powered. 3.7.3. Food The relation between food and energy is two‐fold: (1) Food is a form of energy through its caloric content, and (2) significant amounts of energy are required in the production of food, starting with the manufacturing of fertilizers and tilling of the land to processing, packaging, storing, and transportation at various stages of food production. The following data is taken from [64] and references therein. Accounting for a 26% waste of edible food, the average American consumed 2,590 calories per day (= 10.84 MJ/day) in 2010. The ratio of energy used for the production of food to the amount of energy in the food is 7.36 to 1 (10.3 quads for food production
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compared to 1.4 quads in the food, in the U.S. in 1999), which amounts to a meager conversion efficiency of 1/7.36 = 14%. Consumption of energy for food‐related activities accounts for nearly 15% of the U.S. energy budget. The breakdown of energy use in the U.S. food system is as follows:
Activity Percentage of energy
consumption
Agricultural production Manufacturing of fertilizers and pesticides 8.6%
21.4% Farm activities 12.8%
Transportation 13.6%
Processing 16.4%
Packaging materials 6.6%
Food retail 3.7%
Commercial food services 6.6%
Household storage and preparation Refrigeration 13%
31.7% Preparation 18.7%
Total 100% Source: [64]
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[24] Manwell, J. F., J. G. McGowan, and A. L. Rogers, 2010: Wind Energy Explained: Theory, Design and Application. 2nd ed., Wiley, 704 pages. [25] U.S. Energy Information Administration – Average Tested Heat Rates by Prime Mover and Energy Source, 2007‐2014 <www.eia.gov/electricity/annual/html/epa_08_02.html> with relative proportions of the fuels from <www.eia.gov/energyexplained/index.cfm?page=electricity_in_the_united_states> [26] Jones, W. D., 2008: How Much Water Does It Take to Make Electricity? IEEE Spectrum, 1 April 2008 (corrected 12 September 2011).. <spectrum.ieee.org/energy/environment/how‐much‐water‐does‐it‐take‐to‐make‐electricity> [27] U.S. Department of Energy – Fuel Economy Information – Where the Energy Goes: Gasoline Vehicles <www.fueleconomy.gov/feg/atv.shtml> [28] Demirdöven, N., and J. Deutch, 2004: Hybrid Cars Now, Fuel Cell Cars Later, Science, Vol. 305, pp. 974‐976. [29] The Engineering Toolbox – Electrical Motor Efficiency <www.engineeringtoolbox.com/electrical‐motor‐efficiency‐d_655.html> [30] Tesla – specs page (for 92% efficiency of Model S electric motor) [31] Tesla – Model S Efficiency and Range, by Elon Musk and J. B. Straubel, 9 May 2012. <www.tesla.com/blog/model‐s‐efficiency‐and‐range?redirect=no> [32] HydrogenTrade.com – Hydrogen Fuel cells <www.hydrogentrade.com/fuel‐cells/> [33] U.S. Department of Energy – Office of Energy Efficiency & Renewable Energy – Types of Fuel Cells <energy.gov/eere/fuelcells/types‐fuel‐cells> [34] U.S. Department of Energy – Energy Efficiency and Renewable Energy – Alternative Fuel Center – Ethanol Feedstocks <www.afdc.energy.gov/fuels/ethanol_feedstocks.html> [35] U.S. Department of Energy – Office of Energy Efficiency & Renewable Energy – Making Algal Biofuel Production More Efficient, Less Expensive <www.energy.gov/eere/articles/making‐algal‐biofuel‐production‐more‐efficient‐less‐expensive> [36] Renewable Energy World – Ethanol from Energy Beets: A Viable Option? By B. Dorminey. April 2014. <www.renewableenergyworld.com/articles/print/volume‐17/issue‐2/bioenergy/ethanol‐from‐energy‐beets‐a‐viable‐option.html> [37] United nations Environment Programme – Environment for Development – Oil palm plantations: threats and opportunities for tropical ecosystems – December 2011 <na.unep.net/geas/getuneppagewitharticleidscript.php?article_id=73> [38] Randolph, J., and G. M. Masters, 2008: Energy for Sustainability – Technology, Planning, Policy. Island Press, 791 pages. [39] Pennsylvania State University – Prof. Ljubisa Radovic – Lecture Notes ‐ Efficiency of Energy Conversion <www.ems.psu.edu/~radovic/Chapter4.pdf>
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[40] U.S. Department of Energy ‐ Industrial Technologies Division – Production of Electricity from Biomass Crops, by Ralph P. Overend (undated) <www.mtholyoke.edu/courses/tmillett/course/geog_304B/7290.pdf> [41] U.S. Department of Energy – Home Heating Systems – Wood Pellet Heating <energy.gov/energysaver/wood‐and‐pellet‐heating> [42] Design Recycle, Inc. – Comparison Chart LED Lights vs. Incandescent Light Bulbs vs. CFLs <www.designrecycleinc.com/led%20comp%20chart.html> [43] Independent Energy, LLC – Energy Efficiency <www.independentenergyllc.com/Efficiency.html> [44] Giannelli, R. A., and E. Nam, 2004: Medium and heavy duty diesel vehicle modeling using a fuel consumption methodology, U.S. EPA National Vehicle and Fuel Emissions Laboratory, Ann Arbor, Michigan, 27 pages. <www3.epa.gov/otaq/models/ngm/may04/crc0304c.pdf> [45] United Nations – Food and Agriculture Organization – Renewable Biological Systems for Alternative Sustainable Energy Production – Chapter 1: Biological Energy Production, by K. Miyamoto (FAO Agricultural Services Bulletin – 128) <www.fao.org/docrep/w7241e/w7241e05.htm#1.2.1 photosynthetic efficiency> [46] Mälardalen University (Sweden) – School of Business – Society & Engineering Degree project – Vanadium Redox Flow Battery, by N. Zimmerman, July 2014, 59 pages. <www.diva‐portal.se/smash/get/diva2:772090/FULLTEXT01.pdf> See Table 1 on Page 4 and references cited in footnotes. [47] Butler, P. C., P. A. Eidler, P. G. Grimes, S. E. Klassen and R. C. Miles, 2000: Zinc/Bromine Batteries, Sandia National Laboratories, 16 pages. <www.sandia.gov/ess/publications/SAND2000‐0893.pdf > [48] Duracell – Zinc‐Air Battery – Technical Bulletin <d2ei442zrkqy2u.cloudfront.net/wp‐content/uploads/2016/03/Zinc‐Air‐Tech‐Bulletin.pdf> [49] Green Car Congress – Zinc‐Air Hybrid Buses Get Closer to Market, 16 August 2016 <www.greencarcongress.com/2004/11/zincair_hybrid_.html> [50] Delft University of Technology (TU Delft) – Enipedia – Tesla Model S Battery <enipedia.tudelft.nl/wiki/Tesla_Model_S_Battery> [51] Gonheim, A. F., 2011: Needs, resources and climate change: Clean and efficient conversion technologies, Progress in Energy and Combustion Science, Vol. 37, pages 15‐51. [52] Chalk, S. G., and J. F. Miller, 2006: Key challenges and recent progress in batteries, fuel cells, and hydrogen storage for clean energy systems, J. Power Sources, Vol. 159, pages 73‐80. [53] Calculation: 75 kJ per mole of H2 required for storage in the metal hydride divided by 285.8 kJ released in combustion per mole of H2 taking into account of the condensation of water = 0.26 = 26%. If the storage penalty is 26%, then the efficiency of the storage process is 74%. The number 75 kJ per mole of H2 is given on page 992 of Zeng, K., T. Klassen, W. Oelerich and R. Bormann, 1999: Critical assessment and thermodynamic modeling of the Mg‐H system, International Journal of Hydrogen Energy, Vol. 24, pages 989‐1004. [54] Calculation: 30 kJ per mole of H2 required for storage in the metal organic framework divided by 285.8 kJ released in combustion per mole of H2 taking into account of the condensation of water = 0.10 =
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10%. If the storage penalty is 10%, then the efficiency of the storage process is 90%. The number 30 kJ per mole of H2 is given on page 16 of Prabhukhot, P. R., M. M. Wagh and A. C. Gangal, 2016: A review on solid state hydrogen storage material, Advances in Energy and Power, Vol. 4(2), pages 11‐22. [55] Akhil, A. A. and multiple other authors, 2013: DOE/EPRI 2013 Electricity Storage Handbook in Collaboration with NRECA, 164 pages + appendices. <www.sandia.gov/ess/publications/SAND2013‐5131.pdf> [56] Keeney, J. W., 2013: Investigation of Compressed Air Energy Storage Efficiency, M.S. Thesis in Mechanical Engineering, California Polytechnic State University, San Luis Obispo CA, 272 pages. <digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=2242&context=theses> [57] The World Bank – World DataBank – World Development Indicators – Electric power transmission and distribution losses (% of output) <databank.worldbank.org/data//reports.aspx?source=2&country=&series=EG.ELC.LOSS.ZS&period=#> [58] U.S. Department of Energy – Energy Information Administration – Office of Oil and Gas – Natural Gas Compressor Stations on the Interstate Pipeline Network: Developments since 1996, November 2007. <www.eia.gov/pub/oil_gas/natural_gas/analysis_publications/ngcompressor/ngcompressor.pdf> [59] Weber, C. L., and H. S. Matthews, 2008: Food‐Miles and the Relative Climate Impacts of Food Choices in the United States, Environmental Science & Technology, Vol. 42, pages 3508‐3513. See Table 1 based on information originating from: Davis, S. C., and S. W. Diegel, 2007: Transportation Energy Data Book: Edition 26; ORNL‐6978; Oak Ridge National Laboratory, Oak Ridge, Tennessee. An updated version of this document exists: Davis, S. C., S. W. Diegel and R. G. Boundy, 2015: Transportation Energy Data Book: Edition 34; ORNL‐6991; Oak Ridge National Laboratory, Oak Ridge, Tennessee. [60] SPIECAPAG Entrepose – Iraq Crude Oil Pipeline Trans Saudi Arabia <www.spiecapag.com/?page=202> [61] Ashby, M. F., 2013: Materials and the Environment, Butterworth‐Heinemann, 2nd ed., 616 pages. [62] U.S. Energy Information Administration – How much electricity does an American home use? <www.eia.gov/tools/faqs/faq.cfm?id=97&t=3> [63] U.S. Energy Information Administration – How much electricity is lost in transmission and distribution in the United States? <www.eia.gov/tools/faqs/faq.cfm?id=105&t=3> [64] University of Michigan – Center for Sustainable Systems – U.S. Food System Factsheet, Publication No. CSS01‐06, October 2015, and references therein. <css.snre.umich.edu/css_doc/CSS01‐06.pdf>